A multilayer printed circuit board so-called a multilayer-built-up wiring substrate is manufactured by a semi-additive method and the like and produced by building up a conductor circuit of copper and the like and an interlaminar resin insulating layer on a resin substrate, so-called a core, of approximately 0.5 to 1.5 mm thickness and reinforced with glass cloths and the like serially in alternate fashion and in repetition. The interconnection of the conductor circuits through the interlaminar resin insulating layer of the multilayer printed circuit board is achieved by a via-hole.
Conventionally, the multilayer-built-up printed circuit board is produced according to a method disclosed in, for example, JP H09-130050 A and the like.
That is, at first a through hole is formed in a copper-laminated laminate substrate bearing a copper foil and successively subjected to an electroless copper plating to complete the plated-through hole. Continuously, the surface of the substrate is etched in a conductor pattern to form a conductor circuit, and on the surface of the conductor circuit, a roughened surface is formed by electroless plating, etching and the like. After a resin insulating layer is then formed on the conductor circuit having the roughened surface, the resultant resin layer is subjected to exposure and development treatment to form an opening part for a via-hole and then the resin layer is subjected to UV curing and main curing treatment to form an interlaminar resin insulating layer.
Further, after the interlaminar resin insulating layer is subjected to roughening treatment by an acid, an oxidizing agent and the like, a thin metal layer is formed thereon and a plating resist is formed on the metal layer, and then thickened by electroplating. After the plating resist is separated, etching is carried out to form a conductor circuit connected with a conductor circuit of the lower layer through the via-hole.
After these processes are repeated, a solder resist layer for protecting the conductor circuit is formed finally and then such part where an opening part is exposed to connect an electronic part such as an IC chip and a mother board is plated and successively a solder bump is formed by printing a solder paste to complete the manufacture of a multilayer-built-up printed circuit board.
In manufacture of such a multilayer-built-up printed circuit board, in the case that a conductor circuit connected with a conductor circuit of a lower layer through a via-hole by carrying out electroless plating and electroplating, the opening part for a via-hole is not completely filled with a metal and as being shown in FIG. 25, a recessed part is formed in the peripheral part of the via-hole. Incidentally, FIG. 25 is a cross-section figure illustrating the cross-section of a via-hole of a conventional multilayer printed circuit board.